Field of the Invention
The present invention is related to the area of opto-mechanical inspection system, and more particularly related to a band drive mechanism for opto-mechanical system that has high precision in rotation, great reliability and durability, no backlash, and no particle contamination.
Description of the Related Art
In opto-mechanical inspection system designs, there is always a requirement or movement to rotate an optical part or component, for example, for measurement or inspection. An exemplary optical component is an optical polarizer, an optical aperture wheel, an optical filter assembly, and an optical compensator. To get an ideal optical inspection resolution, it is very critical to perform the rotation with very high precision (minimum backlash or no backlash at all). Further, the drive mechanism shall be of great reliability and durability. For the optical components under laser beams, if a rotation driving mechanism creates some particles in its movement process, the particles would fill in the gaps of the movement driving pair, such as gear pair or cam pair, causing dimension errors onto the rotation components. As a result, the transmission accuracy is affected. If the driving mechanism needs lubricant to be applied onto the driving parts, it would create contamination on the surface of the optical component, then causing defects to the optical component being moved. Currently, most typical optical component rotation driving mechanisms are using gear-pair, chain drive, cable drive, or cam-pair. These types of driving methods have the typical dis-advantages or issues mentioned above when used in the OPTO-mechanical inspection system. Hence there is a need for an optical component driving mechanism to be free of any contamination, both particles and lubricant.
In a traditional rotation driving mechanism, gear-pair driving is widely used. Due to its mechanical nature of the driving principle, there is tooth-tooth meshing error due to the dimension tolerance of the gears. The backlash between the gear-pair shall happen even using anti-backlash gears, which could affect the rotation accuracy commonly required in an opto-mechanical inspection system. Further, due to the friction between the meshing surfaces of the gear-pair, particles are often generated when rotation happens. The particles become another source of the dimension errors of the gear surface. To decrease the friction between the surfaces of gears, oil or other lubricant are often applied in the gear-pair. The applied lubricant is a contamination source to damage the cleanness of the optical component surface. Besides these issues, the friction on the gear surface causes wears to the gears, which affects the life of the gear-pair. On considering the above-mentioned issues or drawbacks, the gear-pair is not an idea rotation driving mechanism for the opto-mechanical inspection system. Similarly, the worm driving mechanism is a special gear driving one and has the similar issues as the gear-pair does.
Timing-belt/pulley, chain/sprocket are other methods often used to drive rotation movements. The timing-belt and pulley drive, although having a relatively low backlash, generate particles in its driving process. These particles will contaminate the environment of the rotation mechanism. These particles can also be dropped onto the surface of an optical component in an opto-mechanical inspection system. Most of the traditional timing belt material is also not suitable for the opto-mechanical inspection system which is always under the exposure of laser beam, and even Ultra-Violet (UV) light or deep Ultra-Violet (DUV) light. On the other hand, due to the structure of the chain/sprocket drive, the sprocket and the chain are not so tightly controlled with their dimensions, the tension of the chain will change after running for a certain period. These characteristics make it very easy to have a big backlash, and the particle issue is another big concern. Accordingly, the chain/sprocket driving mechanism is not suitable for the opto-mechanical inspection system.
Cam driving is a typical friction driving mechanism, it can transform a linear movement into rotation. It relies on the friction between the cam and the cam follower to pass a driving movement. This process generates particles easily. There is often a need to lubricate the cam follower, which can be a source to contaminate the surface of the optical component. Some band driving mechanism such as Timothy David Puckett's band driving mechanism used in telescope rotation system relies on the friction between the band and the pulley, which has the particles issue as well. The rotation driving mechanisms are not suitable in an opto-mechanical inspection system.
Cable rotation drive has been found in many applications. In general, it has low or no contamination, and is relatively low or of no backlash if the cable material is of high quality. The cost of the special required cable material is of a concern in some driving applications.
In this disclosure, a novel band drive rotation mechanism is described. One of the advantages, objectives and benefits of the band drive rotation mechanism is of high precision in rotation, great reliability and durability, and has no backlash and no particle contamination.